Technical Abstract:
The genotype of Salmonella enterica serovar Enteritidis was correlated with phenotype using DNA-DNA microarray hybridization, ribotyping, and Phenotype MicroArrayTM to compare three strains that differed in colony morphology and phage type. No DNA hybridization differences were found between two PT13A strains that varied in biofilm formation; however, ribotype patterns were different. Both PT13A strains had DNA sequences similar to bacteriophage Fels2, whereas the PT4 genome that they were compared to, as well as a
PT4 field isolate, had DNA sequence with some similarity to bacteriophage ST64b. Phenotype MicroArray indicated that the two PT13A strains and the PT4 field isolate had similar respiratory
activity profiles at 37°C. However, wild-type S. enteritidis PT13A grew significantly better in 20% more of the 1920 conditions when assayed at 25°C than did the biofilm-forming PT13A strain. Statistical analysis of respiratory activity suggested that PT4 S. enteritidis had a temperature-influenced dimorphic metabolism that at 25°C somewhat resembled the profile of the biofilm-forming PT13A strain, but that at 37°C was nearly identical to wild-type PT13A.
Although it is possible that lysogenic bacteriophage alter the balance of phage types on-farm by either lytic competition or by altering the metabolic processes of the host cell in subtle ways, the different physiologies of the S. enteritidis strains correlated most with minor, as compared to major, genomic change. These results strongly suggest that the pandemic of egg-associated human salmonellosis that came into prominence in the 1980s is primarily an example of bacterial adaptive radiation impacting the safety of the food supply.